1. Field of the Invention
This invention relates to a cooling device for use in an engine.
2. Description of the Related Art
A conventional cooling device for use in an engine having a cylinder block and a cylinder head is, for example, disclosed in the Japanese Patent Laid Open No. 59(1984)-180024. The cooling device of this type comprises a water jacket, a radiator connected to the water jacket through a piping and a water pump which circulates the cooling water. The cooling device is filled with the cooling water. After the cooling water in the water jacket absorbs the heat from the cylinder block and the cylinder head, the heated cooling water is transmitted to the radiator. The heated cooling water is cooled down by means of the radiator and the cooling water is again supplied to the water jacket.
In the above prior art, the cooling device which utilizes an evaporative cooling method is also disclosed. According to the evaporative cooling method the cylinder block and the cylinder head are cooled down by transferring heat which evaporates the cooling water in the water jacket. Thus, the cooling water boils and changes into the steam. The steam is cooled down and changes into the cooling water in a condenser and the cooling water is again supplied to the water jacket by the water a pump. In the evaporative cooling method, a quantity of the cooling water may be small and the size of the radiator may be reduced because the heat of vaporization is larger than the heat which is absorbed by the water in the liquid type system.
However, in the case where the evaporative cooling method is arranged within the conventional engine, the portion of the water jacket exposed to the air is not sufficiently cooled down. Furthermore, the water jacket should be arranged to prevent rust. Thus, the evaporative cooling method requires the reconstruction of the water jacket as disclosed in the Japanese Patent Publication No. 61-48617, for example.